Get a large but shallow plastic container or pan, 10 bucks or so at Kmart, Walmart. You modded? Might want to consider using a shift kit if you've been thinking about it. If not is ok too.
What's the condition of the fluid now? Red still? Brown?
When you unbolt the pan, work towards one corner without fully removing the pan and allow the fluid to drain out to the plastic container some. Try to get the pan off without much moving around so when it's down you can just look around in the pan for anything unusual. The magnet in the corner of the pan will have small fine particles (black) which is normal. You don't want to see metal pieces though. If the gasket is original, the reusable rubber gaskets are better, just clean the old gasket off, don't be afraid, clean it good for the new gasket, do the surface of the tranny where the pan attaches as well.
I don't remember the torque spec for putting the bolts back, but seat the bolts + 1/4 turn should be good. Once all the bolts are tightened, put at least 6 quarts of fluid back... 7 is ok too just go slow and check the dip stick when 6-1/2 quarts are in and slowly add. You must bring tranny up to temp as well to fill accurately with final top off. This means filing close and driving a little, maybe around the block a bit, shifting through gears and such. Then checking and filling until correct.
Just a word on the tranny fluid, it's SLIPPERY stuff, lol, try not to spill it.
